During development of a fetus in utero, blood is generally oxygenated by the mother's placenta, not the fetus' developing lungs. Most of the fetus' circulation is shunted away from the lungs through specialized vessels or foramens that are open during fetal life, but generally close shortly after birth. Occasionally, however, these foramen fail to close and create hemodynamic problems, which may ultimately prove fatal unless treated.
One defect that may occur is a patent foramen ovale (“PFO”) or patent ductus arteriosus (“PDA”), which may occur between the left and right atria of the heart. During fetal life, an opening called the foramen ovale allows blood to pass directly from the right atrium to the left atrium (bypassing the lungs). Thus, oxygenated blood from the placenta may travel through the vena cava into the right-atrium, through the foramen ovale into the left atrium, and from there into the left ventricle for delivery via the aorta to the fetus' body. After birth, the foramen ovale is replaced with a membrane called the fossa ovalis, and over time, a solid mass of tissue may form.
Occasionally, this membrane and tissue mass fail to form or completely close the foramen ovale, which may be fatal if untreated. Similar defects may occur in other regions within a septum between chambers of the heart, such as atrial septal defects, ventricular septal defects, and the like.
To close such defects, open surgery may be performed to ligate and close the defect. Such procedures are obviously highly invasive and pose substantial morbidity and mortality risks.
Alternatively, catheter-based procedures have been suggested. These may involve introducing umbrella-like structures into the heart that include opposing expandable structures connected by a hub. One of the expandable structures is inserted through the defect, and both are expanded to secure the tissue surrounding the defect between the structures in an attempt to seal and close the defect. Such structures, however, involve frame structures that support membranes, both of which may fail during the life of the patient being treated, opening the defect, and/or releasing segments of the structure within the patient's heart.
Accordingly, apparatus and methods for closing patent foramen ovale, patent ductus arteriosus, or other septal defects would be considered useful.